Tosefta sobre Maasserot 2:12

One who buys dried figs with the intention of pressing them [into fig cakes], [or] dates with the intention of making them into honey -- Rabbi Meir says, he may not eat from them casually or tithe them as Demai, and the Sages say, he may eat from the casually and tithe them as Demai. Rabbi Meir concedes to the Sages that one who takes ears of corn with the intention of processing them, [or] grapes with the intention of making wine from them, [or] olives with the intention of making oil from them, he may eat from them casually, and the Sages concede to Rabbi Meir that with [respect to] fruits, which do not need to 'finish their work' [to become liable for tithes (see Maasr. 2:4)], that he should not eat from them casually.

[If the owner of a field] said to him, "Go out and gather figs for yourself from the fig tree," he may eat casually from them and tithe them as certainly untithed produce. [If he] said to him, "Go out and fill yourself up this basket," he may eat from them casually and tithe them as Demai. In what case does this apply? With [a field belonging to] an am ha'aretz, but with [the field of] a chaver, he may eat and there is no need to tithe, the words of Rebbi. Rabban Shimon ben Gamaliel says, In what case does this apply? With [the field of] an am ha'aretz, but with [the field of] a chaver, he should not eat until he has tithed, since chaverim are not be suspected of taking Terumah [on behalf of other produce] that is not in close by (and thus we can be certain that the chaver-owner would not have already tithed these figs (see Ter. 4:3)). Said Rebbi (not "Rabbi Yehuda"), my words are preferable to the words of Rabban Shimon ben Gamaliel. It is better that chaverim will take Terumah [from produce] that is not close by and not feed untithed produce to amei ha'aretz.

[If the owner of a field] said to him, "Go out and gather figs for me from that fig tree," he (the gatherer) may eat [casually] and need not be concerned about being subject to the laws of stealing. [If he said to him,] "Go out and fill this basket up for me," behold he should be concerned about being subject to the laws of stealing. In either case, he may remove Terumah and tithes from [the basket] on behalf of the field owner's [produce], and he need not be concerned.

[If the owner of a field] said to him, "Go out and gather for yourself twenty figs from within my [field], and I will fill my belly [with figs] from your [field]," the one who gathers by quantity is liable, and the one who "fills his belly" is exempt. Rabbi Eliezer bar Rabbi Tzadok (alt., "bar Rabbi Shimon," MSS Erfurt) says, one who has three figs inside his mouth at the same time is exempt [from tithes], but four -- behold -- he is liable. [If the owner] said to him, "Go out and collect for yourself a big basket," that means [a basket of] no less than a seah; "a medium [basket]," that means no less than a tarkav (three kavs, see Jastrow), "a small [basket]," that means no less than two kavs.